1. Field of the Invention
This invention relates to a mine roof support system and more particularly to a plurality of extensible prop members arranged in pairs with each pair being operable to support a horizontal truss member in engagement with the mine roof where the pairs of prop members are connected by telescoping devices to thereby provide a movable roof support system of a preselected length.
2. Description of the Prior Art
It is known in the practice of continuous mining to provide a temporary roof support above a mining machine, such as a continuous miner operating at the mine face so that roof support is provided for the continuous miner being operated between the mine face and the last section of the mine roof supported by conventional devices such as roof bolts, timbers or the like. The temporary roof support must be operable to continuously support the mine roof as the miner advances into the mine face. This permits uninterrupted operation of the miner without encountering delays in the dislodging operation necessitated by assemblying and disassemblying temporary roof supports.
As illustrated in U.S. Pat. 2,795,935, moving roof supports are known to protect the mining machine and the operator while maintaining a roof support as the mining machine advances the face. A plurality of units are tandemly positioned in the passageway and extend from the mine face to a preselected distance rearwardly therefrom. Each unit includes a pair of roof support engaging elements that extend transversely across the mine passageway. Extensible upright jack devices support the roof engaging support elements adjacent the opposite ends. Each pair of roof engaging support elements includes a forward and rearward roof engaging support element and the upright jack devices associated with each pair are connected by extensible devices to permit walking or relative advancement or retraction of one roof engaging support element relative to the other for each pair. Similar moving roof support devices are illustrated and described in U.S. Pat. Nos. 2,795,936 and 3,890,792.
With the moving roof supports of the type disclosed by the above patents, the various members of the roof support are continuously subjected to bending forces such as for example the telescoping devices which connect the lifting jacks for the roof engaging support elements as the upright jacks advance relative to one another. In addition, torsional forces imparted to the roof engaging support elements subject the upright jacks to bending forces which may render the upwright jacks inoperable to maintain the roof engaging support elements in contact with the mine roof. There is need for a mine roof support system adaptable to provide roof support adjacent the mine face and as material is continuously dislodged from the mine face in which the roof support system is operable to advance at the rate of the dislodging operation.